PPT FINAL

A Project presentation onCharacterization of Anticlastic Effect

in Foil Air BearingsUnder the guidance of Mr. V. Ravi KumarKartik Babu BL.EN.U4MEE09027Linto P Lalu BL.EN.U4MEE09031Mohit Jain BL.EN.U4MEE09034N M Amit BL.EN.U4MEE09035

What is a Bearing?A bearing is a machine element which supports another moving

machine element (known as journal). It permits a relative motion between the contact surfaces of the members, while carrying the load.

Introduction to Foil Air Bearings

Foil bearings were first developed in the late 1950s by AiResearch Mfg. Co.

They were first tested for commercial use in United Airlines Boeing 727 and Boeing 737 cooling turbines.

Most commonly used for high speed, high temperature applications.

AdvantagesHigher ReliabilityNo frequent MaintenanceSoft FailureEnvironmental DurabilityHigh Speed Operation High Temperature Capabilities Process Fluid Operations

Disadvantages

Lower load carrying capacity than roller or oil bearingsWear during start-up and stoppingHigh speed required for operationWobbling of the rotating element

Concept and WorkingWhen shaft rotates, air pushes the

foil away from the shaft, so there is no more contact.

The shaft and foil are separated by the formation of air wedge.

No external pressurization system required (i.e. Aerodynamic bearings).

Air Wedge FormationFor most fluids, with increase in operational

temperature there is a drop in viscosity.Viscosity of air increases with increase in

temperature.Air becomes viscous at the journal - foil

interface, increasing the load carrying capacity.

Anticlastic EffectWhen a plate is subjected to pure bending, the

strains developed in the direction of the load develops a negative strain in the perpendicular direction which is proportional to Poisson’s ratio of the material. This negative strain develops a bending moment in the direction perpendicular to that of the applied bending. This bending in the perpendicular direction to that of the applied bending is termed as anticlastic effect. This effects are also observed in beams.

Problem Definition

The foils on the bearing can be modeled as a cantilever with a UDL in the direction perpendicular to the surface of the screen.

At high speed operation, the side profile of the foil gets deformed which causes eccentric rotation of the journal in the bearing resulting in shaft/journal wobbling.

Pressure Distribution

The anticlastic effect on the bearing foil gets affected by varying the following parameters: Length Width Thickness

Parameters Effecting Anticlastic Effect

Analytical SimulationUsing the CAE software package ‘Ansys’ the model was simulated in the following steps:PreferencesPreprocessor

Element type Material Properties Sections Modelling Meshing Loads

SolutionGeneral Post Processor

Ansys Simulated Model

Experimental Setup

Validation of Analytical Simulation done experimentally.Apparatus Used:Rigid support to hold foil0.45mm thickness Copper sheetNylon Thread1.5Kg weight

Loading Procedure

Validation Copper foil, 300mm x 75mm x 0.45 mm

Distortion along z axis Distortion along z axis in mm Experimentally in mm Analytically

-14.69 -13.9401-15.09 -14.6302-14.77 -14.9249-14.58 -14.9999-14.84 -14.9732-14.51 -14.9162-14.46 -14.8676-14.55 -14.8458-14.7 -14.857-14.3 -14.8981

-15.55 -14.9553-15.26 -14.998-14.91 -14.967-14.72 -14.7611-14.45 -14.2257 -16

-15.5

-15

-14.5

-14

-13.5

-131 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Experimental vs. Analytical

Length Variation

Length: 180mmWidth: 60mmThickness: 0.25mmDistortion Deflection: 0.9619mm


Inference:The trend tells that as length approaches width, the max deflection keeps reducing.



Length Vs. Anticlastic DistortionBeCu, Width 60mm, Thickness 0.25mm

Length in mm Anticlastic Distortion in mm60 0.184590 0.4257120 0.654150 0.8318180 0.9619240 1.2158300 1.5029360 1.8023

0

0.5

1

1.5

2

60 90 120 150 180 240 300 360

Length Vs. Anticlastic Distortion

Width Variation keeping length as 180mm

Width: 30mmThickness: 0.25mmDistortion Deflection: 0.9011mm




Width Vs. Anticlastic Distortion (Length 180mm)

BeCu, Length 180mm, Thickness 0.25mmWidth in mm Distortion Deflection in mm

30 0.901145 0.912260 0.961975 1.000690 0.9804120 0.8505150 0.6924180 0.5529 0

0.2

0.4

0.6

0.8

1

1.2

30 45 60 75 90 120 150 180

Width vs Distortion Deflection








30 1.202245 1.201260 1.215875 1.260590 1.3189120 1.307150 1.1845180 1.0267240 0.7373 0

0.2

0.4

0.6

0.8

1

1.2

1.4

30 45 60 75 90 120 150 180 240

Width Vs. Distortion Deflection








30 1.502845 1.500360 1.502975 1.519790 1.5617120 1.6629150 1.6337180 1.5179240 1.2044300 0.9216

00.20.40.60.8

11.21.41.61.8

30 45 60 75 90 120 150 180 240 300

Width Vs. Distortion Deflection

Length/Width Variation

Decreasing Deflection

Increasing Deflection

Decreasing Deflection

InferenceMinimum deflections occur when the width is taken to be

equal to the length, i.e., when it approaches a ‘Square Profile’Confirming results observed in length variation discussed

previously

Thickness Variation

Thickness: 0.25mmLength: 240mmWidth: 60mmDistortion Deflection: 1.2158mm

Thickness: 0.4mmLength: 240mmWidth: 60mmDistortion Deflection: 1.2167mm

Thickness: 1mmLength: 240mmWidth: 60mmDistortion Deflection: 1.2221mm

Thickness: 2mmLength: 240mmWidth: 60mmDistortion Deflection: 1.2325mm

Thickness vs. Anticlastic Distortion

BeCu, Length 240mm, Width 60mmThickness in mm Distortion Deflection in mm

0.25 1.21580.3 1.21610.4 1.21670.5 1.21751 1.2221

1.5 1.22712 1.2325

1.2051.21

1.2151.22

1.2251.23

1.235

0.25 0.3 0.4 0.5 1 1.5 2

Thickness Vs. Distortion Deflection

Alternative Solution Using multiple bearings in series



Inference When two separate bearings are utilized, the anti-clastic

deflection reduces drasticallyReduces wobbling of the journal.

Future Scope Giving negative anticlastic curvature to the edge of foil plate. Conducting fluid flow analysis to analyze the formation of air

wedge. Using alternative alloys of superior properties to develop new

generation of foil air bearings

THANK YOU

PPT FINAL

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